1. Field of the Invention
This invention relates to a method of measuring unsaturated inductances of an equivalent circuit of a synchronous machine for obtaining unsaturated values of inductances in the equivalent circuit of a synchronous machine.
2. Discussion of Background
A synchronous machine is mainly utilized as a generator or a motor always running at a predetermined revolution number. Reactances in these machines are generally utilized for calculating a limit of an output, a stability or the like. Accordingly, an inductance (inductance multiplied by 2.pi.f is reactance) treated as a value viewed from an armature such as a synchronous reactance or a transient reactance, attracts attention.
For instance, various test methods are described in "the Abstract of Test Methods for a Synchronous Machine (Parts 1 to 4)" (issued by the Institute of Electrical Engineers of Japan) summarizing test methods of the synchronous machine, for measuring inductances of the synchronous machine. However, no description is found in the abstract concerning a method of measuring values of elements constituting an equivalent circuit of the synchronous machine, such as an armature leakage inductance, a field leakage inductance, a direct-axis damper leakage inductance, a direct-axis armature reaction inductance, a quadrature-axis damper leakage inductance and a quadrature-axis armature reaction inductance, based on a unified theory.
Accordingly, these values are obtained by combining known methods, when the values of the respective elements constituting the equivalent circuit of the synchronous machine are necessary. For instance, one method is as follows.
First, a direct-axis synchronous reactance is obtained based on results of a no-load saturation characteristic test and a three-phase short-circuit characteristic test. The direct-axis armature reaction reactance is determined by subtracting a value of the armature leakage reactance from the above value. In this occasion, an assumed value is often adopted as the value of the armature leakage reactance. To actually measure the armature leakage reactance, it is necessary to draw out a rotor thereof and provide additional wirings, which requires considerable time and labor.
Next, a direct-axis transient reactance is obtained by a three-phase sudden short-circuit test. A parallel value of the direct-axis armature reaction reactance and the field leakage reactance is obtained by the above value substracted by the value of the armature leakage reactance. Furthermore, the field leakage reactance is separated from the parallel value.
Similarly, a direct-axis initial transient reactance is obtained by the three-phase sudden short-circuit test. A parallel value of the direct-axis armature reaction reactance, the field leakage reactance and the direct-axis damper leakage reactance is obtained by subtracting the value of the armature leakage reactance from the above value. Furthermore, the direct-axis damper leakage reactance is separated from the parallel value.
The respective reactances concerning the quadrature-axis, are obtained as follows. First, a quadrature-axis synchronous reactance is obtained by a measurement result by the slip method. The quadrature-axis armature reaction reactance is determined by subtracting the value of the armature leakage reactance from the above value.
Next, a quadrature-axis initial transient reactance is obtained by a measurement result by Dalton-Cameron method. A parallel value of the quadrature-axis armature reaction reactance and a quadrature-axis damper leakage reactance is obtained by subtracting the value of the armature leakage reactance from the above value. Furthermore, the quadrature-axis leakage reactance is separated from the parallel value.
In the meantime, there is a vector control capable of controlling with high accuracy, as a control method of the synchronous machine. To perform the vector control, it is necessary to set detailed values of the respective elements constituting the equivalent circuit of the synchronous machine to a control device, as motor constants. Accordingly, in cases of driving the synchronous machine by the vector control, the respective reactance values has previously been obtained by the above method, which are set to the control device.
Since the method of measuring unsaturated inductances of the equivalent circuit of the synchronous machine, is as above, the high accuracy of the respective reactance values can not be expected. That is, the above method is a combination of available measuring methods such as in measuring the no-load saturation characteristic, which is not a method based on a unified theory. Accordingly, it is impossible to investigate influence of the respective values on a total measurement accuracy.
Furthermore, since the actual measurement of the armature leakage reactance is not easy, an assumed value is apt to be adopted as the value, which causes lowering of the measurement accuracy. Furthermore, the synchronous machine having a large capacity controlled by the vector control, is often driven at a rated frequency of about 2 to 10 Hz. In case of such a low rated frequency, as a result of the three-phase sudden short-circuit test, a number of waves contained in a waveform becomes less, and it becomes difficult to read the direct-axis transient reactance and the direct-axis initial transient reactance from the waveform.
Furthermore, to carry out the slip method test, it is necessary to drive the rotor at a speed slightly different from a speed of a revolving field of a stator. Accordingly, when a size of the synchronous machine which is an object of the test, is enlarged, a three-phase power source on the side of the stator, a driving motor on the side of the rotor and the like become large-scale ones. In performing the test, a skilled driving operation is required to stably maintain a low slip. A pulsation in a revolution number caused by an influence of a reaction torque, or a too much slip causes measurement errors.
In the conventional method stated as above, there is a high possibility of containing errors in the measurement values. Furthermore, much labor and time are required in the measurement.
When the motor constants of the control device in the vector control, are to be set, optimum values should be set since the set values considerably influence on accuracy of a control calculation. Since the accuracy of the measurement value by the above method, is poor, an operation of setting optimum motor constants by repeating a driving operation wherein the control device and the synchronous machine are combined, is required. The time and the expense required for the operation are enormous in case of a large capacity machine.